Today, most of the heavy hydrocarbon oil produced from Canadian oil sands (known as bitumen), in particular, Athabasca oil sands, is obtained via surface mining followed by extraction with a water-based system built on a discovery made in the 1920s and known as the Clark process. Upon extraction of the bitumen, a frothy water-hydrocarbon mixture must be separated. Thereafter, the hydrocarbon product obtained is too viscous to pump and is frequently diluted with an organic material to render a bitumen-solvent blend (also known as dilbit or synbit) pumpable. This bitumen-solvent is pumped, i.e., pipelined, directly to a facility for upgrading to the desired product mix, e.g., liquid fuel such as jet fuel, diesel and gasoline. The Clark process, despite many decades of process improvement work, remains energy intensive and is environmentally detrimental in that it requires significant quantities of water that must be cleaned for re-use, and generates significant bottoms components that contain high levels of fines (also referred to as tailings or tailings fluid fines).
Tailings fluid fines from the water-based Clark extraction of bitumen from Canadian oil sands require long-term storage before they can become trafficable and suitable for reclamation. The Energy Resources Conservation Board (ERCB) of the Canadian province of Alberta has noted in Directive 074 (February, 2009) that “in past applications, mineable oil sands operators proposed the conversion of fluid tailings into deposits that would become trafficable and ready for reclamation. While operators have applied fluid tailings reduction technologies, they have not met the targets set out in their applications; as a result, the inventories of fluid tailings that require long-term containment have grown. With each successive application and approval, public concerns have grown.” In one region of interest, in Alberta, Canada, there are already several huge operations using this technology wherein the water requirements are supplied by the Athabasca River.
In spite of the environmental concerns of using the water-based Clark extraction process, there is additional consideration of importing into the U.S. greater quantities of the bitumen-solvent blend product produced from the process. Currently under consideration is a proposed pipeline that would connect oil resources in Alberta, Canada, to refineries on the Texas coast. As reported in http://www.npnorg/2011/09/01/140117187/for-protesters-keystone-pipeline-is-line-in-tar-sand, “The 1,700-mile long Keystone XL, as it's called, would help our friendly northern neighbor expand development in one of the largest, but dirtiest, sources of oil on the planet. It's bound up in hardened formations called tar sands, and it's not easy to extract.”
Due to the many environmental concerns in extracting and transporting bitumen from oil sands, replacement of the water-based Clark extraction process with hydrocarbon-based solvents has been investigated. The attractive nature of using a hydrocarbon-based solvent is that little if any water would be needed in such a process.
U.S. Patent Pub. No. 2009/0294332 discloses, for example, an oil extraction process that uses an extraction chamber and a hydrocarbon solvent rather than water to extract the oil from oil sand. The solvent is sprayed or otherwise injected onto the oil-bearing product, to leach oil out of the solid product resulting in a composition comprising a mixture of oil and solvent, which is conveyed to an oil-solvent separation chamber.
U.S. Pat. No. 3,475,318 discloses extracting tar low in asphalenes from a tar sand that contains asphaltenes The tar sand is treated with a saturated hydrocarbon solvent having from 5 to 9 carbon atoms per molecule or with a solvent containing saturated hydrocarbons having from 5 to 9 carbon atoms per molecule and up to 20 percent aromatics having 6 to 9 carbon atoms per molecule. Treatment can be carried out using a variety of filters, such as a continuous belt filter, moving pan filter or rotary pan filter. The treated tar sand is steam stripped to remove solvent from the treated tar sand.
U.S. Pat. No. 4,347,118 discloses a solvent extraction process for tar sands wherein a low boiling solvent having a normal boiling point of from 20° to 70° C. is used to extract tar sands. The solvent is mixed with tar sands in a dissolution zone, the solvent:bitumen weight ratio is maintained from about 0.5:1 to 2:1. This mixture is passed to a separation zone in which bitumen and inorganic fines are separated from extracted sand, the separation zone containing a classifier and countercurrent extraction column. The extracted sand is introduced into a first fluid-bed drying zone fluidized by heated solvent vapors, so as to remove unbound solvent from extracted sand while at the same time lowering the water content of the sand to less than about 2 wt %. The treated sand is then passed into a second fluid-bed drying zone fluidized by a heated inert gas to remove bound solvent. Recovered solvent is recycled to the dissolution zone.
U.S. Patent Pub. No. 2010/0130386 discloses the use of a solvent for bitumen extraction. The solvent includes (a) a polar component, the polar component being a compound comprising a non-terminal carbonyl group; and (b) a non-polar component, the non-polar component being a substantially aliphatic substantially non-halogenated alkane. The solvent has a Hansen hydrogen bonding parameter of 0.3 to 1.7 and/or a volume ratio of (a):(b) in the range of 10:90 to 50:50.
U.S. Patent Pub. No. 2011/0094961 discloses a process for separating a solute from a solute-bearing material. The solute can be bitumen and the solute-bearing material can be oil sand. A substantial amount of the bitumen can be extracted from the oil sand by contacting particles of the oil sand with globules of a hydrocarbon extraction solvent. The hydrocarbon extraction solvent is a C1-C5 hydrocarbon. The particle size of the oil sand and the globule size of the extraction solvent are balanced such that little if any bitumen or extraction solvent remains in the oil sand.
Although hydrocarbon extraction processes provide an advantage in that water is not used in the extraction of the oil from the oil sand, thereby reducing a portion of the environmental impact, problems in using hydrocarbon-based extractions persist. For example, disclosed processes have typically relied on solvents that are substantially pure hydrocarbons. Since there is at least some solvent loss during extraction, additional quantities of the solvent have to be obtained externally, which substantially adds to the overall cost of obtaining the desired crude oil product. In addition, disclosed processes have generally been demonstrated to extract all or substantially all of the bitumen from the oil sand. This results in a crude oil product that is extremely viscous, high in undesirable metals and asphaltenes content and is rather difficult to pipeline and upgrade to fuel grade products. Although use of hydrocarbon solvents can recover substantial amounts of the bitumen, the resulting crude composition, which also comprises the hydrocarbon solvent, is substantially similar to the current dilbit or synbit. Such a product will not necessarily allay the concerns of pipelining the product through the proposed Keystone XL.